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Circuit Diagram – Gas Leakage Detector using Arduino with GSM Module

Assemble the circuit as shown in diagram! Important connections are explained below.A photograph of the assembled circuit is shown below.

Note:- The speaker is not shown in this photograph. Anyway you can wire the speaker as shown in circuit diagram and connect it to pin 8 of arduino.

Important Aspects about the Program

When we develop critical systems like Gas Leakage Detector or similar systems like Fire Alarm System, we need to monitor the sensor parameters continuously(24×7). So our system must monitor “gas leak” continuously.This is achieved by scanning the sensor output (digital out of MQ5) continuously inside the ScanGasLevel() subroutine. If you look into the program, the main function loop() has only two subroutines – CheckGas() and CheckShutDown() – which are called repeatedly. CheckGas() – is a subroutine which scans sensor output continuously and take actions if there occurs a ‘gas leak’ at any point of time. CheckShutDown() – is a subroutine to monitor the shut down process and check if status of room is back to normal conditions (no gas leaking).

CheckGas() – is the function which monitors occurrence of a gas leak 24×7. This function fetches the gas level measured by MQ35 (by reading digital out of MQ35 using digitalRead() command) and stores it to the variable Gas_alert_val for comparison. If there is no ‘gas leak’ – the sensor out will be HIGH. If there occurs a ‘gas leak’ at any point of time, the sensor out will immediately change to LOW status. The statement if(Gas_alert_val==LOW) checks this and if a gas leak occurs, then an inner subroutine SetAlert() will be invoked.

SetAlert() is the function that controls number of SMS alerts sent to each mobile number loaded in the program. The number of SMS alerts sent can be altered by changing the stopping condition of while loop. The stopping condition sms_count<3 – means 3 SMS alerts will be sent to each mobile number. If you want to send 5 alerts, just change the stopping condition to sms_count<5 – you got it ? The function to send SMS (using AT Commands) – SendTextMessage() will be called 3 times if SMS alert count is 3. This function SendTextMessage() will be invoked as many times as the number SMS alerts set in the program. In addition to sending SMS alerts, this subroutine also controls the sound alarm. The alarm is invoked using command digitalWrite(speaker,HIGH) – which will activate the speaker connected at pin 8 of arduino.

Note:- We have limited the number of SMS alerts using the stopping condition. Once a gas leak occurs and the set number of SMS alerts has been sent, the system will not send any more SMS! The system assumes that its job is over by sending SMS. Humans has to come and shut down the gas leak problem. After sending alerts, the system will start monitoring Shut Down process. Once the gas leak has been eliminated, system will automatically reactivate its SMS alert settings by resetting the sms_count variable back to zero.

The output after applying ‘gas leak’ is shown in photograph!

Here is a video demonstration of the output!

CheckShutDown() – is the function which monitors if gas leak was shut down. We need to entertain this function only if a ‘gas leak’ has occurred. To limit the entry to the statements inside this routine, we have introduced a variable Gas_Leak_Status. This variable value will be set to value 1 when a gas leak occurs (check the statement inside SetAlert()). The statements inside CheckShutDown() will be executed only if the value of Gas_Leak_Status==1. (If there was no gas leak occurred, we don’t need to waste time executing ShutDown checking statements). We consider the ‘gas leak’ has been eliminated once room temperature is back to normal. So if our variable Gas_shut_val falls back to HIGH status, we consider gas leak has been eliminated and surroundings are safe. The subroutine has statement to stop the gas leakage alarm (refer statement – digitalWrite(speaker,LOW) – which cuts the supply to pin 8 of arduino and stops the sound alarm) which will be executed when gas leak is eliminated completely (as the status of Gas_shut_val == HIGH). We start our Gas Leakage monitoring again with SMS Alerts active! (We reset the Gas_Leak_Status variable and sms_count variable back to zero – which are essential variable conditions for monitoring gas leak again and to send alert sms if gas leak repeats.